Status: Accidental in fall.
Documentation: Photograph: 14 Sep 2019 Perkins Co (https://ebird.org/checklist/S59808685).
Taxonomy: No subspecies are recognized.
See related taxonomic discussions under Mallard and Mottled Duck.
Whether Mexican Duck is a valid species is a matter of debate. It is considered by some authors, including AOU (1998), a subspecies (as A. p. diazi) of Mallard, A. platyrhynchos (see also Johnsgard 1975, Sibley and Monroe 1990). AOU denied a proposal by Banks to elevate it to species status citing a study by Hubbard (1977) who concluded there was “extensive introgression” with Mallard in the northern parts of Mexican Duck’s range; the AOU discussion can be found HERE. However, the evidence provided in Hubbard in support of this concluson is at best equivocal: on a scale of 0-36 (“pure” Mexican Duck = 36) the scores ranged from 34.5 at the southern edge of its range to 28.3 in the north. While this shallow cline suggests Mallard introgression at some time in the past (McCracken et al 2001, Avise 1990) and to an uncertain extent currently (Lavretsky et al 2015, Leukering and Mlodinow 2012), recent studies have found assortative mating in areas where Mallard occurs with Mexican Duck (Bevill 1970, Webster 2006, Baldassarre 2014). Genetic studies by Lavretsky et al (2015) suggest that Mexican Duck and Mallard are in the early stages of divergence; mtDNA and Z-chromosome data show significant differentaton, “perhaps at a level that would warrant species recognition”. Very few Mallards occur in the breeding range of Mexican Duck during periods when pairing occurs (Baldassarre 2014, Leukering and Mlodinow 2012). For these reasons, we follow the decision of Gill and Donsker (2017) to elevate Mexican Duck to full species status. While there is evidence that American Black, Mottled, and Mexican Ducks all possess some degree of Mallard introgression, taxonomic consistency would also indicate treatment of Mexcan Duck as a full species (Leukering and Mlodinow 2012, Drilling et al 2020).
14 Sep 2019 Perkins Co, photographs Steve Mlodinow and Dave Ely (https://ebird.org/checklist/S59808685).
Comments: The above record was of a bird with Mallards in a small pond near Grant, Perkins Co. The description provided follows: “Overall, it had a dark brown body contrasting somewhat sharply with paler head and neck. The underparts were uniformly dark from chest thru undertail coverts. The tail was entirely brown. The speculum looked to have narrower borders than that of a MALL, more so to the rear than in front. The head and neck were pale brown with blackish on crown and with a blackish eyeline. No black mark at gape. No pale tan unstreaked area as in MODU. The bill was orange with dusky along culmen and towards tip. No distinct black blotches.”
There are two older reports, neither accepted (Bray et al 1986, Silcock et al 1986). A specimen referred to as Mexican Duck was collected 17 Oct 1921 in Cherry Co (Bent 1923). This is a female #973 in the Field Museum of Natural History, Chicago, but is now considered likely a hybrid between Mallard and American Black Duck (David Willard, personal communication). The second report is of an adult male shot in Rock Co 19 Oct 1969 (Menzel 1970). Although its identity as a Mexican Duck was confirmed by Paul Johnsgard and the bird showed no evidence of captivity, the possibility of its being an escaped bird could not be eliminated (Menzel 1970). Menzel (1970) noted that at that time Mexican Ducks were kept in captivity in Hall Co and that escapes occurred occasionally. A dark bird paired with a Mallard 20 Jun 1993 Sioux Co (Grzybowski 1993), may have been a Mottled Duck or Mexican Duck.
There are numerous records for Colorado, east to Yuma and Kiowa Cos, adjacent to Nebraska (CBRC 2017, eBird.org accessed December 2019) but none for Kansas (Thompson et al 2011, eBird.org accessed December 2019).
American Ornithologists’ Union [AOU]. 1983. The AOU Check-list of North American birds, 6th ed. Allen Press, Lawrence, Kansas, USA.
Baldassarre, G. 2014. Ducks, geese, and swans of North America. Johns Hopkins University Press, Baltimore, Maryland, USA.
Bellrose, F.C. 1976. Ducks, Geese & Swans of North America. Stackpole Books, Harrisburg, Pennsylviania, USA.
Bent, A.C. 1923. Life histories of North American wild fowl. Bulletin of the United States National Museum 126. Dover Publications Reprint 1962, New York, New York, USA.
Bevill, W.V., Jr. 1970. Effects of supplemental stocking and habitat development on abundance of Mexican Ducks. Master’s thesis, New Mexico State University, Las Cruces, New Mexico, USA.
Bray, T.E., B.K. Padelford, and W.R. Silcock. 1986. The birds of Nebraska: A critically evaluated list. Published by the authors, Bellevue, Nebraska, USA.
Colorado Bird Records Committee [CBRC]. 2017. Mottled Duck records. Colorado Bird Records Committee database, accessed November 2017.
Drilling, N., S. O. Williams III, R. D. Titman, and F. McKinney (2020). Mexican Duck (Anas diazi), version 1.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.mexduc.01.
Hubbard, J.H. 1977. The biological and taxonomic status of the Mexican Duck. Bull. New Mexico Dept. Game Fish 16.
Johnsgard, P.A. 1975. Waterfowl of North America. University of Indiana Press, Bloomington, Indiana, USA.
Lavretsky, P., J.M. DaCosta, B.E. Hernandez-Banos, A. Engilis Jr., M.D. Sorenson, and J.L. Peters. 2015. Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards. Molecular Ecology 24: 5364–5378.
Leukering, T., and S.G. Mlodinow. 2012. The Mexican Duck in Colorado: Identification and Occurrence. Colorado Birds 46: 296-309.
McCracken, K.G., W.P. Johnson, and F.H. Sheldon. 2001. Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula). Conservation Genetics 2: 87-102.
Menzel, K.E. 1970. Mexican Duck. NBR 38: 89-90.
Sibley, C.G., and B.L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, Connecticut, USA.
Silcock, W.R., T.E. Bray, and B.K. Padelford. 1986. Mexican Duck in Nebraska. NBR 54: 40-41.
Thompson, M.C., C.A. Ely, B. Gress, C. Otte, S.T. Patti, D. Seibel, and E.A. Young. 2011. Birds of Kansas. University Press of Kansas, Lawrence, Kansas, USA.
Webster. R. 2006. The Status of Mottled Duck (Anas fulvigula) in Arizona. Arizona Birds Online 2: 6-9.
Silcock, W.R., and J.G. Jorgensen. 2020. Mexican Duck (Anas diazi), Version 1.0. In Birds of Nebraska — Online. www.BirdsofNebraska.org
Birds of Nebraska – Online